Thermal damage (burn) in carburized and hardened precision gear steels caused by grinding was investigated. Excessive grinding temperatures cause grinding bum and result in excessive scrappage. AISI 9310 and X53 gear steels, used in helicopters and tilt-rotor aircraft, respectively, were prepared and heat-treated by a production partner. Grinding tests were conducted on these steels. Nital etching was used to detect grinding burn. Models were established to predict onset of thermal damage for AISI 9310 and X53 steels based on specific grinding energy determined from grinding force measurements. The models were compared to results published for other steels.

When machining hardened steel (≥ 45 HRC) with polycrystalline cubic boron nitride (PCBN) tooling, the cutting speeds used produce high temperatures in the primary shear zone, which are sufficient to plasticise the workpiece. The paper initially reviews the effect of workpiece hardness and cutting speed on chip formation, workpiece surface integrity and cutting forces. Equations are detailed for determining the primary shear zone temperature, the proportion of heat conducted into the workpiece and the shear flow stress. Following on from this, experimental work is presented involving the orthogonal machining of AISI H13 hot work die steel with PCBN tooling. Tests were carried out over a range of cutting speeds with workpieces of different hardness, in order to provide cutting force, shear angle, chip morphology and primary shear zone thickness data. The shear flow stress decreased with increasing cutting speed and/or workpiece hardness. With the AISI H13 heat treated to 49±1 HRC, the stress magnitude changed more significantly with cutting speed and the proportion of heat conducted away from the workpiece approached 99% at 200 m/min. Shear localised chips were produced with white unetched layers due to intense heat generation followed by rapid cooling.

The orthogonal machining process when end turning medium carbon and austenitic stainless steels with cemented WC-Co tools coated with single-layer (TiC), two-layer (TiC/TiN), and three-layer (TiC/Al 2 O 3 /TiN) hard thin films was investigated. Extensive experimental investigations including the thermal, mechanical and tribological responses of the tribo-contact between the coating-substrate system and the chip, under different cutting conditions, were carried out. The study sheds light on the cutting forces, the interface temperatures and the tribo-contact conditions, including the fxictional heat flux conducting into either the chip or the insert, the mean coefficient of sliding friction and the contact loads exerted on the tool rake face. Finally, it was demonstrated how the intrinsic coating properties control the heat flux flowing into both components of such a closed tribo-system and the mechanical stresses on the contact area.

A quasi-two zone predictive model developed in the present work for the prediction of the combustion processes in dual fuel engines and some of their performance features. Methane is used as the main fuel while employing a small quantity of liquid fuel (pilot) injected through the conventional diesel fuel system. This model emphasizes the effects of chemical kinetics activity of the premixed gaseous fuel on the combustion performance, while the role of the pilot fuel in the ignition and heat release processes is considered. A detailed chemical kinetic scheme consists of 178 elementary reaction steps and 41 chemical species is employed to describe the oxidation of the gaseous fuel from the start of compression to the end of expansion process. The associated formation and concentrations of exhaust emissions are correspondingly established. This combustion model is able to establish the development of the combustion process with time and the associated important operating parameters such as pressure, temperature, rates of energy release and composition. Predicted values for methane operation show good agreement with corresponding previous experimental values over a range of operating conditions mainly associated with high load operation.

Development of air-cooled absorption cycles appropriate for residential applications has been problematic. This study examines an ammonia-water triple effect cycle known as the kangaroo cycle, and investigates its limitations when used as an air-cooled space air conditioner. The triple effect absorption processes were modeled and a methodology for optimizing the design was developed. The arrangement and relative sizes of the heat exchangers thermally coupling the upper and lower loops were studied. The thermal coupling involves the upper rectifier, condenser, and absorber rejecting heat to the lower generator. Contrary to other triple effect studies, internal generator heat exchangers were incorporated in both the upper and lower generators and their optimum relative positions were studied. Also, errors of up to 150 percent were shown to result from conventional LMTD and pinch point analysis due to the highly non-linear temperature-enthalpy relationship in the upper condenser. Three configurations for the upper heat exchangers coupling the upper loop to the lower generator were analyzed, and their relative sizes were optimized. The cycle’s performance was shown to depend on the exit temperature of the lower loop generator, and the COP optimization was demonstrated with respect to this design variable. Operation at air-cooled ambient conditions was investigated. At lower ambient temperatures that are heavily weighted in air conditioning rating standards, the efficiency is very favorable. Equipment development and cost issues need to be addressed.

This paper presents a design and off-design study of a geothermal field consisting of a number of wells, a steam network which collects the geothermal fluid, and a power plant to generate electricity. The geothermal field considered is located in Italy and the fluid is a mixture of steam and non-condensable gases. The power plant is a conventional type for vapor dominated fields and has a compressor-extractor to remove non-condensable gases from the condenser. The condenser has wet cooling towers to remove heat. In this study, computer codes developed at the University of Perugia were used to simulate the behavior of geothermal field as a whole. The wells are modeled with second order functions in order to describe pressure-flow rate and temperature-flow rate correlations. The geothermal fluid network is calculated by setting pressures and thermal losses in all the branches. The power plant is simulated with all its components: steam turbine, condenser, gas extractor, cooling towers and auxiliaries. All the components of the geothermal field are simulated at both design and off-design conditions. The fluid network is solved with an algorithm developed by the authors, which allows the definition of boundary conditions by means of curves based on experimental data. The advantage in comparison with conventional techniques, requiring a fixed pressure or flow rate as boundary condition, is that the solution of the network and the power plant is always a real solution. The results show how changes in ambient conditions or in the characteristic curve of one or more plant components may influence power production and the exploitation of the geothermal source.

This paper presents a design process for a dual solar/gas fired generator. A generator fired by solar energy and/or natural gas for a water-lithium bromide absorption chiller of 25 refrigeration tons (RT) was modeled. The natural gas is considered as the backup heat when the solar energy is unavailable or insufficient. The flue gas and the water-lithium bromide solution are in co-current flow, while the solar fluid and the water-lithium bromide solution are in counter-current flow. Fifty fluted tubes were installed vertically between two concentric cylindrical tubes. A solid ceramic insert was used to enhance heat transfer on the gas side that is considered as having the dominant heat transfer resistance. The burner is installed inside the smaller cylindrical tube. The solar fluid from the solar collector enters the generator through the fluted tubes while the water-lithium bromide mixture flows in the annular channel around the fluted tubes as a subcooled liquid. The generator is divided into two regions according to the heat transfer mechanism: subcooled liquid region and desorption region. In this model, a simultaneous solar and gas fired desorption process was investigated. The amount of makeup heat needed from natural gas was determined as a function of the solar fluid flow rate. Local temperature profiles were predicted by the model.

Battelle has developed a mesoscale combustor/evaporator that provides a lightweight and compact source of heating, cooling, or energy generation for both man-portable and stationary applications. The device uses microscale flow channels that increase the available surface area for heat transfer and reduce the fluid boundary layer. These characteristics in turn result in heat fluxes for hydrocarbon/air combustion in excess of 25 W/cm 2 and thermal efficiencies of 80 to 90%. Furthermore, high heat transfer rates allow for short channels and reduced pressure drops. Recent development efforts have focused on obtaining low emissions and improving the combustor/evaporator fabrication process. By using spatially varying stoichiometry inside the combustor, catalyst coated microchannels, and increased coolant temperature, the combustor’s CO and NO x emissions were reduced to below California standards for hot water heaters and boilers. The fabrication process photochemically machines thin metal laminates and then uses diffusion bonding to form a monolithic component. This approach is capable of high fin aspect ratios and can be scaled up for mass production.

The paper presents the results of an optimization study of an automotive fuel cell propulsion system equipped with a fuel reformer. Based on a set of fuel cell polarization curves determined experimentally by running a prototype fuel cell stack at a variety of operating pressures and temperatures, a numerical steady state model was used to determine the optimal operating pressure and temperature. The optimization criteria were the size of individual components and the entire propulsion system as well as its total efficiency at both full power and partial load. The results suggested that an automotive system should be operated at relatively high pressure (308 kPa), but an expander must be used to recover most of the power used for compression. A surprising result of this analysis is that a relatively low temperature (∼60°C) results in smallest heat rejection equipment if neutral water balance is mandated. The efficiency of the system is about 33% at full power and about 38% at 25% of the load. Higher efficiencies may be achieved by selecting a higher fuel cell operating voltage, but that would result in larger fuel cell stacks, which may be a limiting factor for automotive application with the state-of-the-art fuel cells.

Absorption chillers are gaining global acceptance as quality comfort cooling systems. These machines are the central chilling plants and the supply for comfort cooling for many large commercial buildings. Virtually all absorption chillers use lithium bromide (LiBr) and water as the absorption fluids. Water is the refrigerant. Research has shown LiBr to be one of the best absorption working fluids because it has a high affinity for water, releases water vapor at relatively low temperatures, and has a boiling point much higher than that of water. The heart of the chiller is the absorber, where a process of simultaneous heat and mass transfer occurs as the refrigerant water vapor is absorbed into a falling film of aqueous LiBr. The more water vapor absorbed into the falling film, the larger the chiller’s capacity for supporting comfort cooling. Improving the performance of the absorber leads directly to efficiency gains for the chiller. The design of an absorber is very empirical and requires experimental data. Yet design data and correlations are sparse in the open literature. The experimental data available to date have been derived at LiBr concentrations ranging from 0.30 to 0.60 mass fraction. No literature data are readily available for the design operating conditions of 0.62 and 0.64 mass fraction of LiBr and absorber pressures of 0.7 and 1.0 kPa. Experiments were conducted on an internally cooled smooth tube 0.01905 m in outside diameter and 1.53 m in length. Tests were conducted with no heat and mass transfer additive. The data, for testing at 0.62 and 0.64 mass fraction of LiBr, were scaled and correlated into both Nusselt (Nu) and Sherwood (Sh) formulations. The average absolute error in the Nusselt correlation is about ±3.5% of the Nu number reduced from the experimental data. The Sherwood correlation is about ±5% of the reduced Sh data. Data from the open literature were reduced to the authors’ Nu and Sh formulations and were within 5% of the correlations developed in the present study. Hence, this study provides correlations for the complex heat and mass transfer process that is validated against extensive experimental data. The study therefore contains useful information for the design of a vertical column absorber operating with no heat and mass transfer additive.

Absorption system have been investigated for many years. However, coefficient of performance COP or heat gain factor HGF for absorption systems are significantly lower than those for conventional compression systems. This has restricted their wide application. This paper discusses the behavior of mixture NH 3 -H 2 O through of an ejector, operating in an absorption heat pump system. This combination improves the performance of conventional absorption system and with the phasing out of ozone-damaging refrigerants, absorption refrigerators, heat pumps and air-conditioning now provide a potential alternative. For the detailed calculation of the proposed system a method has been developed, which employs analytical functions describing the thermodynamic properties of die mixture. The influence of three major parameters: generator, condenser and evaporator temperature, on ejector efficiency and heat gain factor of the system is discussed. Also the maximum value of HGF was estimated by correlation of above three temperatures.

The potential benefits of external combustion hot air engines: quietness, combustion cleanliness and combustion efficiency, as well as multi-fuel usage, can be realized only if the heat of the combustion gases is efficiently transferred into the working fluid. Heat transfer in external combustion power systems is usually accomplished by a single, relatively large heat exchanger and by a large delta T across the heat exchanger, which leads to poor First and Second Law efficiencies. The basic flaw in the conventional analysis of externally heated power cycles is identified. A novel open cycle external combustion power system described here incorporates constant pressure recuperation and isothermal expansion for power generation, as in a classical Ericsson cycle. The cycle is improved by the use of exhaust heated isothermal combustion and heat transfer into an immediately adjacent isothermally heated expander. Isothermal expansion is compared with adiabatic expansion. It is shown that a fixed value of specific work can be produced at a lower expander inlet temperature with isothermal expansion than with adiabatic expansion. The thermodynamic as well as practical advantages of this lower temperature are noted. The cycle efficiency is shown to be further improved by isothermal combustion. A practical embodiment of the proposed power system in the form of a hot air turbine will be described. Engine performance, in terms of specific power and system efficiency as a function of temperature and expansion ratio, is predicted with realistic assumptions of component efficiencies and system losses.

A new theory is presented, termed the vapor surfactant theory, which explains the heat and mass transfer enhancement mechanism of additives in absorption chillers. The vapor surfactant theory holds that the enhancement additives are surfactants delivered to the surface of the solution film from the vapor and that they produce enhancement by generating intense secondary flows on the film. The secondary flows, driven by surface tension gradients (Marangoni convection), augment the transfer process by providing mixing of the film. The primary variable in the enhancement is the surface concentration distribution of the surfactant additive since the surface tension gradients arise due to non-uniformities in the surface concentration. The vapor surfactant theory is found to explain all observations from several different types of experiments. The new theory is a significant departure from past theories in its emphasis on the primary role of the vapor in the process.

This study involves the experimental verification of a universal heat exchanger accumulator design procedure. A heat exchange accumulator was manufactured according to a mathematical model developed by the authors and installed into a small air conditioning system. Experimental results show that the addition of the heat exchanger accumulator results in a liquid overfeeding operation that replaces the previously utilized direct expansion operation. It provides an improved air conditioning system that has a 7.5% increase in coefficient of performance and a 4.4% increase in refrigerant mass flow rate. A pressure ratio reduction has a positive effect on the compressor performance and life span. Liquid overfeeding increases the cooling capacity of the system by 6.5%. When compared to direct expansion systems, this basic heat exchanger accumulator provides a reduction in cycling losses and power consumption, an increase in suction pressure and an improvement in isentropic compressor efficiency.

The computer code ABSIM has been developed for simulation of absorption systems in a flexible and modular form, making it possible to investigate various cycle configurations with different working fluids. Based on a user-supplied cycle diagram, working fluid specification and given operating conditions, the program calculates the temperature, flowrate, concentration, pressure and vapor fraction at each state point in the system and the heat duty at each component. The modular structure of the code is based on unit subroutines containing the governing equations for the system’s components. A main program calling these subroutines links the components together according to the cycle diagram. The system of equations for the entire cycle is thus established, and a mathematical solver routine is employed to solve them simultaneously. Property subroutines contained in a separate database serve to provide thermodynamic properties of the working fluids. The paper describes the current capabilities and recent improvements made to ABSIM along with examples of simulation results for several rather complex cycles, including lithium bromide-water double-, triple- and quadruple-effect cycles and ammonia-water GAX, branched GAX and vapor exchange (VX) cycles.

Simulations for thermal characterization of electronic packages for silicon-based integrated circuit (IC) components typically assume one of the two uniform heat generation conditions. They are: (1) an isoflux condition in which heat generation is uniformly distributed over the active surface of the die, or (2) a uniform heat generation over the entire (or active) volume of the die. The use of these models may be justified due to high thermal conductivity of silicon, size of the devices on the die, and their relatively uniform spatial distribution over the entire surface of the die in the traditional silicon technologies. However, the current and future technologies are migrating towards embedded systems solutions, such as system-on-chip, and in traditional applications devices are brought in close proximity to each other for improved on-chip electrical performance. These trends result in localized regions of power dissipation on the die that would invalidate the use of traditional uniform generation models in the thermal characterization. The present study examines the effect of discrete heat sources (as opposed to uniformly distributed sources) on the die on thermal performance and characterization of the electronic packages. For this purpose, a conjugate heat transfer problem of a memory chip in a 119 I/O flip chip ceramic and plastic ball grid array (FC-C & PBGA) package under natural and forced convection conditions. First the model is validated against experimentally measured thermal data on a 119 I/O FC-C & P BGA daisy-chain test packages with a thermal test die with uniformly distributed resistive heat source. Junction-to-ambient temperature difference predictions from the simulations are within 10% of the measurements for the uniform heating case. The validated model is then suitably modified to account for discrete heat sources and actual substrates. Results from the discrete heat sources study show a 15–20% increase in predicted junction-to-ambient temperature difference and a larger (a 10–15 °C) temperature variation across the active face of the die than for with a uniform heat source. These results call for the use of discrete heat sources in the thermal characterization of new generation of embedded silicon technologies. They also point to the need for development of test die and characterization methodologies for these technologies with discrete heat sources.

In pure heat transfer, specifications of effectiveness, fluid properties, and flows enable calculation of the heat exchanger area. In the case of falling film absorption, a simultaneous heat and mass transfer governs the performance of the absorber. The exchange of mass across the liquid-vapor interface involves the generation of heat. The heat effects associated with the mass exchange increase the temperature, which affects the equilibrium state of the pressure and composition and in turn affects the mass. The falling film flow rate coupled to the physical properties of kinematic viscosity and surface tension govern the flow regime of a vertical falling film. Wavy-laminar, roll-wave laminar, and turbulent flows will develop convective contributions that can enhance the transfer of mass into the film. The combined interaction of all these factors makes the absorption process very difficult to analyze and predict. A study of simultaneous heat and mass transfer was therefore conducted on a vertical falling film absorber to better understand the mechanisms driving the heat and mass transfer processes. Falling films are characteristically unstable, and a wavy-laminar flow was observed during the experimental study. The wavy flow further complicates the problem; therefore, only limited information is known about the temperature and concentration profiles along the length of the absorber that describe the local heat and mass transfer rates. Hence, this study presents much-needed experimental data on the heat and mass transfer processes in the absence of heat and mass transfer additive. Absorption experiments were conducted in a mini-absorber test stand at various falling film flow rates, at various absorber pressures, and with various compositions of the binary salt solution. Thermographic phosphors were successfully used to measure the temperature profile along the length of the absorber test tube. These measures of the local variations in temperature enabled calculation of the bulk concentration along the length of the absorber. The bulk concentration varied linearly, from which one may infer that the concentration gradient in the direction of flow is approximately constant. The implication is that the mass flux, and therefore the absorber load, can be solved for by using a constant flux approximation.

Battelle, Pacific Northwest Division (Battelle) and Pacific Northwest National Laboratory 1 (PNNL) are developing a miniature absorption heat pump. Targeted applications include microclimate control ranging from manportable cooling to distributed space conditioning. The miniature absorption heat pump will be sized to provide 350 W t of cooling 2 . A complete manportable cooling system, which will include the microscale heat pump, an air-cooled heat exchanger, batteries, and fuel, is estimated to weigh between 4 and 5 kg. For comparison, alternative systems weigh about 10 kg. Size and weight reductions in the microscale heat pump are possible because the device can take advantage of the high heat and mass transfer rates attainable in microscale structures.

In this paper I present the results of my studies on a new explanation of the vortex (Ranque-Hilsch) tube’s phenomenon. It is new way of understanding this process. The vortex tube was discovered in 1930 by French physicist Georges Ranque. Hilsch was the first American engineer to develop this phenomenon into practical, effective cooling solutions for industrial applications and theoretical modeling and calculations. Currently, the use of conventional vortex pipes is limited in engineering application because of their low thermodynamic efficiencies. Problems associated with these thermal limitation include the separation of gaseous condensate, the separation of liquified air, and more. Still, some technological studies on heat energy generation using new techniques and heat transformation devices should be conducted. This paper addresses the subject of the Ranque-Hilsch vortex tube’s phenomenon explanation based on a vortex-exited oscillation. There is no previous work reported in the literature desdribing the temperature splitting model by wave generating process. The study was motivated by the heating and cooling phenomenon that occurs in the Ranque-Hilsch vortex tube.

This paper shows how to obtain the complete recovery of exhaust heat in the context of a gas turbine power plant. The power plant uses partial combustion of the fuel and yields power and a synthesis gas for further use in a chemical plant or conventional steam power plant. The key is a heat exchanger in conjunction with a Ni/NiO chemical loop that alters the composition of the air stream so that there is nearly a perfect match of the hot and cold streams down to ambient temperature. The chem-loop removes the oxygen for fuel combustion from the air as it raises the temperature of both the water/air and the synthesis gas streams (only the latter is used for power production). Assuming no heat losses from unit operations, no parasitic losses, and a pinch of only 2°C (simultaneous boiling and condensing) the First Law efficiency of the power plant can be over 98% (Second Law is about 45%). There are no acidic stack gases to contend with at this point as the partially combusted fuel is then exported for other uses, its value diminished only by the amount of power produced.